A 71-year-old Alzheimer's patient has been sentenced to six months in prison in Houston, Texas, after confessing to murdering her husband 30 years ago.

The short sentence angered the victim's family, who believed it was too lenient, but given her confession, deteriorating health and a lack of other evidence, lawyers agreed to a plea deal.

Police had long suspected Carolyn Krizan-Wilson was responsible for the shooting death of her husband Roy McCaleb in their home in 1985, but never had the evidence to prosecute.

Krizan-Wilson, who had been married seven times, was convicted of bigamy following the McCaleb's death when it was revealed she was still married to another man at the time.

In 1985, she told police that a barefoot homeless man who had previously raped her, tracked her down, broke into the couple's home and shot her sleeping husband, according to prosecutors.

Krizan-Wilson stuck to that story until Wednesday when she entered a guilty plea and signed a judicial confession, admitting she shot McCaleb.

She was charged with murder in 2008, but a judge dismissed the indictment. In 2012, an appeals court reinstated the murder charge and a court date was set for next month before a plea deal was struck.

Prosecutor Bill Exley told ABCNews.com that Krizan-Wilson was only recently diagnosed with Alzheimer's disease and dementia and "there were never any questions about her competency. Her own defense lawyer and the judge agreed."

Krizan-Wilson, for instance, drove herself routinely to and from court and aided in her own defense, Exley said.

"Her age and her medical condition, I think all sides realized this was probably the right and just decision to make for all parties," said defense attorney Stafford James, according to ABC affiliate KTRK-TV.

McCaleb's family, however, was angered by what they believed was too short a sentence and that Krizan-Wilson will not begin serving time until the day after Christmas.

"One day, she's going to have to talk to God and she's going to have to face what she did," Pamela McCaleb Nalley, the victim's daughter, told reporters. "There are higher powers."